I have a well maintained all original 1990 crx hf with 120k miles on it but the last 2 full tanks ive given it, it only got 33mpg before the gas needle went below red. It had a full tune up but one place said i should check to see if it has ngk spark plugs (honda's original option) It has been sitting a lot since i only drive it about once or twice every 2 weeks in the city but I really want to know what i can do. NO check engine lights on or anything either.
Check the tailpipe to see if the inside is coated with a dry black soot. That would mean that you are running too rich (like jadziasman said) and likely need a new oxygen sensor.
It could also be a bad coolant sensor telling the the computer that the engine is always cold so it injects more fuel than needed.
It can be throwing a code without the cel coming on. Is your ecu flashing when the car is running. It's under the carpet in front of the passengers seat...
Could be a bad o2 sensor, could be a torn diaphragm in the fuel pressure regulator, could be an injector stuck open, could be that it's summer and you started using a/c... blah, blah blaahhh...
We would be more helpful if you give us more info. on what's going on.
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